The invention relates to a method for forming a finely divided polymerizate, further to a fine powder consisting of a finely divided polymerizate of this kind as well as to a use of the fine powder.
In the manufacture for example of fiber compound materials, in particular of unidirectionally fiber reinforced thermoplastics, or of powder lacquers, polymerizate particles are required which are finely divided and which consist of so-called high performance polymers. Three kinds of method are known for producing a fine powder which consists of a finely divided polymerizate: 1. grinding, which is particularly suitable for crystalline polymers (e.g. PPS or PEEK).xe2x80x942. Dispersion polymerization or dispersion poly-condensation, in which a polymer in the form of a finely divided powder arises (e.g. polyamide). 3.xe2x80x94Subsequent dispersion of polymerizates, with particles being produced by means of spraying, reprecipitating or emulsification or also combinations of method steps of this kind.
The object of the invention is to create a method for the particular polymer polyetherimide, which has an amorphous, i.e. non crystalline form, or similar polymers such as for example polycarbonate, polyamidimide or polyethyleneterephthalate in which a finely divided polymerizate arises which is suitable for the manufacture of fiber compound materials by means of pressure impregnation of strands which are formed of endless fibers. This object is satisfied by the method which is defined in claim 1.
The method for forming a finely divided polymerizate in the form of a dispersion of particlesxe2x80x94for the purpose of manufacturing powder lacquers or fiber compound materialsxe2x80x94comprises two steps:
1) In a first step a solution of a polymer, which is dissolved in a first liquid, is emulsified in a second liquid. The polymer is not soluble in the second liquid. The first liquid has a lower boiling point than the second and it is soluble in the second only to a limited extent. Owing to the limited solubility the polymer remains dissolved in the droplets which arise during the emulsification. Under the influence of mechanical meansxe2x80x94in particular of a high speed stirring apparatusxe2x80x94and by shear forces caused by the latter, droplets are formed, the average diameter of which corresponds to one of the named uses and is preferably less than 0.03 mm.
2) In a second step the first liquid is removed by distillation from the mixture while retaining the emulsion, so that the polymer solidifies in the form of particles, in particular spheroid polymer particles.
Subordinate claims 2 to 8 relate to advantageous embodiments of the method in accordance with the invention. The subjects of claims 9 and 10 are a fine powder and a use of a dispersion of finely divided polymer particles in the manufacture of fiber compound materials respectively.